JP2010094156A - Mri apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate selection of a coil element which achieves PI (Parallel Imaging) imaging of a desired multiple speed rate and updating of a scanning plan for the PI imaging. <P>SOLUTION: When performing the PI imaging using a multi-channel coil having a plurality of coil elements provided in a PF coil unit 30, a PI imaging determination part 9 determines whether or not the PI imaging of a desired multiple speed rate is possible on the basis of the information of the scanning plan set by pilot imaging and the array information of the coil elements configuring the multi-channel coil. Then, when determining that it is possible, a transmission/reception part 3 executes the PI imaging on the basis of MR signals detected from the coil elements. Meanwhile, when determining that it is impossible, the PI imaging determination part 9 automatically updates the scanning plan to be updated or reports it at a display part 7, and the PI imaging is executed on the basis of the scanning plan which is automatically updated or updated by an operator who receives the report. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an MRI apparatus, and more particularly to an MRI apparatus that enables parallel imaging using a multichannel coil.

  In magnetic resonance imaging (MRI), a nuclear spin in a subject tissue placed in a static magnetic field is excited by a high-frequency signal (RF pulse) having the Larmor frequency, and a magnetic resonance signal ( This is an imaging method for reconstructing image data from MR signals.

  An MRI apparatus is an image diagnostic apparatus that generates image data based on MR signals detected from within a living body, and obtains a lot of diagnostic information such as biochemical information and functional diagnostic information as well as anatomical diagnostic information. Therefore, it has become indispensable in the field of diagnostic imaging today.

  In recent years, various high-speed imaging techniques for shortening the image data generation time have been developed along with the practical use of MRI apparatuses capable of collecting three-dimensional image data. As one of the methods, a high-speed imaging method called parallel imaging (Parallel Imaging) imaging using a multi-channel coil having a plurality of RF coils as coil elements has been proposed (see, for example, Patent Document 1). According to this method, first, a plurality of RF channels are formed by bundling a plurality of MR signals collected by thinning out the phase encoding step based on a predetermined algorithm, and then reconstructing the MR signals of this RF channel By developing the plurality of image data obtained in this manner based on the sensitivity distribution data of the RF channel, it is possible to generate unfolded image data in a short time.

  Conventionally, an MRI apparatus collects MR signals necessary for generating one piece of image data by repeating the sequence while sequentially updating the phase encoding, and the MR signal acquisition time is much larger than the number of phase encoding updates. It depends. Therefore, it takes a lot of time to collect MR signals necessary for generating image data having clinically effective image quality and imaging range (FOV), making high-speed imaging difficult.

  In order to solve such problems, a multi-echo type sequence for detecting a plurality of MR signals within an RF pulse repetition period and a high-speed imaging method using a sequence with a shortened repetition period have already been developed. However, these high-speed imaging methods have a problem in that image contrast deterioration and image distortion are likely to occur.

On the other hand, in parallel imaging imaging (hereinafter referred to as PI imaging), a multi-channel coil having a plurality of coil elements is used as described above, and a sequence in which phase encoding steps are thinned out at equal intervals is executed. By reducing the number of steps, the time required for collecting MR signals is shortened. At this time, a folding phenomenon occurs in the image data obtained by reconstructing the MR signal collected by thinning out the phase encoding step. This folding phenomenon bundles the MR signals from the coil elements. Can be removed by a development process based on the sensitivity distribution data of the RF channel formed. If the number of RF channels in the phase encoding direction is N, the maximum shortening rate of time required to collect MR signals due to the reduction of the number of phase encoding steps (hereinafter referred to as the maximum double speed rate) is 1 / N. .
JP 2004-329613 A

  In PI imaging, a multi-channel coil in which a plurality of coil elements are two-dimensionally arranged in a body axis direction (z direction) and a direction perpendicular to the body axis direction (x direction) is usually the subject. They are arranged near the body surface and near the back surface, respectively. These coil elements are divided into a plurality of sections in the body axis direction, and the plurality of coil elements in each section are arranged in the x direction. At this time, the maximum double speed ratio in the PI shooting includes information on the scan plan for PI shooting set in advance in the image data for positioning by pilot shooting, a plurality of sections set by the operator, and a plurality of coils included in these sections. Determined by element-based RF channel.

  However, conventionally, when the operator sets a desired speed ratio prior to PI shooting, the desired speed ratio is set without considering the PI shooting scan plan. It was not done. For this reason, it is sometimes impossible to collect diagnostic image data by PI imaging, or diagnostic image data having a low S / N ratio or unacceptable artifacts may be generated. After resetting sections and RF channels in the coil, it was necessary to redo the acquisition of MR signals and the generation of diagnostic image data by reconstruction processing.

  That is, when setting the desired double speed ratio without considering the scan plan for PI imaging, the inspection efficiency and diagnostic accuracy in PI imaging greatly depend on the skill of the operator, and it takes a lot of time to set the optimal section and RF channel. However, there is a problem that not only the inspection efficiency is remarkably lowered but also the burden on the operator is increased.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain a desired double speed ratio when performing PI shooting based on a scan plan set in advance by image data for positioning by pilot shooting. An object of the present invention is to provide an MRI apparatus capable of easily selecting a suitable RF channel and updating a scan plan.

  In order to solve the above-mentioned problem, the MRI apparatus of the present invention according to claim 1 is configured to irradiate an object to which a static magnetic field and a gradient magnetic field are applied with an RF pulse, and to detect the object detected by a plurality of coil elements. In an MRI apparatus for performing parallel imaging (PI) imaging based on MR signals of a plurality of RF channels formed by synthesizing MR signals from a plurality of RF channels, the MR signals detected by the coil elements are synthesized MR signal synthesis means for forming the image, scan plan setting means for setting a scan plan for PI imaging with respect to positioning image data collected in advance by pilot imaging for the subject, and setting a desired double speed ratio for the PI imaging Speed ratio setting means for performing, information on the scan plan for PI photography, and the RF channel selecting means for selecting the plurality of RF channels suitable for the PI imaging from the plurality of RF channels formed by the MR signal synthesizing means based on information on the desired double speed ratio. It is a feature.

  According to the present invention, when performing PI imaging on the subject based on a scan plan set in advance by positioning imaging data by pilot imaging, selection of a suitable RF channel that enables a desired double speed ratio and scan plan Can be easily updated. Therefore, efficient PI shooting can be performed without depending on the skill of the operator.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the MRI apparatus of the present embodiment described below, when PI imaging is performed by arranging a multichannel coil in which a plurality of coil elements are two-dimensionally arranged near the body surface and the back surface of a subject, an image for positioning by pilot imaging It is determined whether or not PI photographing at a desired double speed ratio (desired double speed ratio) is possible based on information on a scan plan for PI photographing set in advance in the data and arrangement information on coil elements constituting the multi-channel coil. judge. If it is determined that PI imaging is possible, a suitable coil element that enables the desired double speed ratio is selected from the plurality of coil elements, and PI imaging is executed. On the other hand, if it is determined that PI imaging is not possible, the scan plan to be updated is automatically updated or notified to the operator, and the coil element is changed based on the PI imaging scan plan updated by the operator who has received the automatic update or notification. Select and perform PI imaging on the subject.

(Device configuration)
The configuration of the MRI apparatus in the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing an overall configuration of the MRI apparatus in the present embodiment, and FIG. 2 is a block diagram showing a specific configuration of an RF coil unit and a transmission / reception unit provided in the MRI apparatus.

  The MRI apparatus 200 shown in FIG. 1 includes a static magnetic field generation unit 1 and a gradient magnetic field generation unit 2 that generate a magnetic field for a subject 150, and an RF pulse that irradiates the subject 150 with an RF pulse and detects an MR signal. The coil unit 30, the transmitter / receiver 3 that supplies a pulse current to the RF coil unit 30 and performs predetermined signal processing on the MR signal detected by the RF coil unit 30, and the top 4 on which the subject 150 is placed And a top plate moving mechanism unit 5 that moves the top plate 4 in the body axis direction of the subject 150.

  Further, the MRI apparatus 200 reconstructs MR signals received by the transmission / reception unit 3 in pilot imaging and PI imaging, and generates an image data generation unit 6 that generates positioning image data and diagnostic image data. Display unit 7 for displaying the image data, setting of MR signal acquisition conditions and image data display conditions, setting of desired double speed ratio, setting of scan plan for PI photographing, selection of scan plan update mode, and various command signals PI imaging at the desired double speed ratio is possible based on the input unit 8 for inputting the information and the like, and information on the arrangement of the coil elements provided in the multi-channel coil 302 (to be described later) in the RF coil unit 30 and information on the scan plan for PI imaging. The PI imaging determination unit 9 that determines sex and the above-described units in the MRI apparatus 200 are integrated. And a Gosuru control unit 10.

  The static magnetic field generation unit 1 includes a main magnet 11 composed of a normal conducting magnet or a superconducting magnet, and a static magnetic field power source 12 for supplying current to the main magnet 11, and is disposed in a photographing field in the center of the gantry (not shown). A strong static magnetic field is formed on the subject 150. The main magnet 11 may be constituted by a permanent magnet.

  On the other hand, the gradient magnetic field generator 2 is provided in each of the gradient magnetic field coil 21 that forms a gradient magnetic field in the body axis direction (z direction) and the x and y directions orthogonal to the body axis direction, and the gradient magnetic field coil 21. On the other hand, a gradient magnetic field power supply 22 for supplying a pulse current is provided.

  The gradient magnetic field coil 21 and the gradient magnetic field power supply 22 add position information to the imaging field in which the subject 150 is placed based on the sequence control signal supplied from the control unit 10. That is, the gradient magnetic field power source 22 controls the pulse current supplied to the gradient magnetic field coils 21 in the x direction, the y direction, and the z direction based on the sequence control signal, thereby forming a gradient magnetic field in each direction. The gradient magnetic fields in the x, y, and z directions are combined to form a slice selection gradient magnetic field Gs, a phase encode gradient magnetic field Ge, and a read (frequency encode) gradient magnetic field Gr that are orthogonal to each other. The gradient magnetic field is applied to the subject 150 while being superimposed on a strong static magnetic field formed by the main magnet 11.

  Next, specific examples of the RF coil unit 30 and the transmission / reception unit 3 shown in FIG. 1 will be described with reference to FIG. The RF coil unit 30 in FIG. 2 includes a whole body coil (WB coil) 301 for both transmitting and receiving provided together with the gradient coil 21 in the gantry (not shown) of the MRI apparatus 200 and the vicinity of the body surface and the back surface of the subject 150. The multi-channel coils 302-1 and 302-2 dedicated for reception are provided. Then, in pilot imaging for the purpose of generating positioning image data, a pulse current having a predetermined frequency (Larmor frequency) and an envelope is supplied to the WB coil 301 and imaging of the subject 150 placed in a high magnetic field. The region is irradiated with RF pulses. The MR signal generated in the tissue of the subject 150 by the irradiation of the RF pulse is detected by the WB coil 301 and supplied to the transmission / reception unit 3.

  On the other hand, in PI imaging for the purpose of generating diagnostic image data, a pulse current having a predetermined frequency and envelope is supplied to the WB coil 301 as in the case of pilot imaging, and the imaging region of the subject 150 is captured. Are irradiated with RF pulses. The MR signal generated in the tissue of the subject 150 by the irradiation of the RF pulse is detected by each of the coil elements two-dimensionally arranged by the multichannel coils 302-1 and 302-2 and supplied to the transmission / reception unit 3. Is done. At this time, each of the multi-channel coils 302-1 and 302-2 forms a plurality (Nz) of sections 3s1 to 3sNz in the body axis direction (z direction), and each of these sections has a plurality ( Nx) coil elements.

  FIG. 3 shows a multichannel coil 302 in which, for example, four (Nx = Nz = 4) coil elements 3e11, 3e12, 3e13, 3e14, 3e21,. As shown in the figure, these coil elements are divided into sections 1 (3s1) to section 4 (3s4) with respect to the z direction, and each of the sections 1 to 4 is 4 with respect to the x direction. There are two coil elements 3ei1 to 3ei4 (i = 1 to 4).

  Returning to FIG. 2, the transmission / reception unit 3 includes a transmission unit 31, a reception unit 32, an MR signal synthesis unit 33, and an RF channel selection unit 34.

  The transmission unit 31 has a function of supplying a pulse current to the above-described WB coil 301 in pilot imaging for collecting positioning image data and PI imaging for collecting diagnostic image data. A pulse current having substantially the same frequency as the magnetic resonance frequency (Larmor frequency) determined by the static magnetic field strength and modulated with a predetermined selective excitation waveform is generated and supplied to the WB coil 301.

  The MR signal synthesis unit 33 includes an amplifier circuit and a switching circuit, and is detected by the coil element 3eij (j = 1 to Nx) in each section 3si (i = 1 to Nz) of the multichannel coils 302-1 and 302-2. MR signals are combined based on a predetermined algorithm to form a plurality of RF channels. Note that the MR signal synthesis unit 33 normally uses the multi-channel coil 302-1 or the like to amplify the MR signal detected by the coil element 3eij (i = 1 to Nz, j = 1 to Nx) at a high S / N. It is provided in the vicinity of 302-2.

  On the other hand, the RF channel selection unit 34 sends the PI shooting scan plan information and the desired double speed ratio information supplied from the input unit 8 through the main control unit 101, and further the main control unit 101 from the RF coil unit 30. M RF channels suitable for PI imaging are selected from a plurality of RF channels formed by the MR signal synthesizing unit 33 based on information of the multi-channel coils 302-1 and 302-2 supplied via .

  The receiver 32 includes a 1-channel pilot imaging receiver and an M-channel PI imaging receiver (not shown). The pilot imaging receiver receives the 1-channel MR signal detected by the WB coil 301 in pilot imaging. Receive and perform signal processing such as intermediate frequency conversion, phase detection, low frequency amplification, filtering and A / D conversion. On the other hand, the PI imaging receiving unit performs the same signal processing as described above on the MR signals in the M RF channels supplied from the RF channel selection unit 34 in the PI imaging.

  Next, the couchtop 4 shown in FIG. 1 is slidably attached in the body axis direction (z direction) of the subject 150 on the upper surface of the bed (not shown), and the subject 150 placed on the couchtop 4 is attached. By moving in the z direction, the imaging target region is set to a suitable position in the imaging field. The top plate moving mechanism unit 5 is attached to, for example, the end or lower portion of the bed, and generates a drive signal for moving the top plate 4 based on a top plate movement control signal supplied from the control unit 10. . Then, the top plate 4 is moved in the z direction at a predetermined speed by this drive signal.

  The image data generation unit 6 includes a data storage unit 61 and a high-speed calculation unit 62, and the data storage unit 61 stores MR data including a plurality of MR signals collected in time series by sequentially changing the phase encoding. An MR data storage unit 611 that stores the image data generated by the MR data reconstruction process.

  The MR data storage unit 611 includes an MR signal group (hereinafter referred to as positioning MR data) at the time of pilot imaging composed of a plurality of MR signals collected in the phase encoding direction by the WB coil 301 and each of the RF channels. The MR signal group (hereinafter, referred to as diagnostic MR data) at the time of PI imaging composed of a plurality of MR signals collected with different phase encodings is stored. In the image data storage unit 612, the positioning image data obtained by reconstructing the positioning MR data, and the diagnostic image generated by performing the reconstruction processing and the expansion processing on the diagnostic MR data are stored. Data is saved. In the PI imaging, diagnostic MR data collected by thinning out the phase encoding step in order to shorten the MR signal collection time is stored in the MR data storage unit 611.

  On the other hand, the high-speed calculation unit 62 of the image data generation unit 6 includes a reconstruction processing unit 621 and a development processing unit 622. The reconstruction processing unit 621 reads positioning MR data stored in the MR signal storage unit 611, performs reconstruction processing by two-dimensional Fourier transform, and generates positioning image data. Further, the reconstruction processing unit 621 sequentially reads the diagnostic MR data of each RF channel stored in the MR signal storage unit 611, performs similar reconstruction processing, and generates diagnostic image data for each of the RF channels. . In each of the diagnostic image data generated at this time, aliasing caused by thinning out of the phase encoding step occurs.

  Next, the expansion processing unit 622 includes a sensitivity map data storage unit (not shown) in which sensitivity map data for each of the RF channels is stored in advance, and a plurality of pieces generated by the reconstruction processing unit 621 for each of the RF channels. The diagnostic image data is developed based on the sensitivity map data, and the aliasing that has occurred in the diagnostic image data is corrected. Note that a specific method of the expansion process is described in Japanese Patent Application Laid-Open No. 2002-315731 and the above-described Patent Document 1, and thus detailed description thereof is omitted.

  The display unit 7 includes a display data generation circuit, a conversion circuit, and a monitor (not shown), and displays the positioning image data and diagnostic image data generated by the image data generation unit 6. That is, at the time of displaying the positioning image data, the display data generation circuit supplies the PI supplied from the input unit 8 via the control unit 10 to the positioning image data supplied from the image data storage unit 612 of the image data generation unit 6. Display data is generated by superimposing information on an imaging scan plan (for example, the position and direction of a slice section in PI imaging). Next, the conversion circuit converts the display data into a predetermined display format in accordance with preset display conditions of the image data, performs D / A conversion, and displays it on the monitor including a CRT or a liquid crystal panel.

  On the other hand, when displaying the diagnostic image data, the display data generation circuit supplies the subject supplied from the control unit 10 to the diagnostic image data after the aliasing correction supplied from the image data storage unit 612 of the image data generation unit 6. Attached information such as information is added to generate display data, and the conversion circuit performs a conversion process similar to the above on the display data and displays it on the monitor.

  Next, the input unit 8 is connected to the display unit 7 via the control unit 10 to form an interactive interface. The console is equipped with various input devices such as a display panel, switch, keyboard, mouse, etc., input of subject information, setting of MR signal acquisition conditions including pulse sequence, setting of image data display conditions, diagnostic image Setting of scan plan for PI photography performed on positioning image data for the purpose of data generation, setting of desired double speed ratio, selection of scan plan update mode, input of top board movement instruction signal, and various command signals Perform input etc. In this embodiment, either the navigation update mode or the automatic update mode is selected when updating the PI photography scan plan.

  The PI imaging determination unit 9 is based on the coil element array information supplied from the RF coil unit 30 via the control unit 10 and the PI imaging scan plan information supplied from the control unit 10. It is determined whether or not PI shooting at the desired double speed ratio set in step 1 is possible. If it is determined that the PI shooting is impossible in the navigation update mode, the scan plan item to be updated to enable the PI shooting is searched, and the search result is displayed on the display unit 7 to display the PI shooting by the operator. Support the update of scan plans. On the other hand, when it is determined in the automatic update mode that the above-described PI shooting is impossible, the PI shooting determination unit 9 automatically updates the scan plan item that disables PI shooting and supplies the update result to the control unit 10. At the same time, it is displayed on the display unit 7.

  Next, the control unit 10 includes a main control unit 101, a sequence control unit 102, and a top board movement control unit 103. The main control unit 101 includes a CPU and a storage circuit (not shown) and has a function of controlling the MRI apparatus 200 in an integrated manner. The storage circuit of the main control unit 101 includes subject information input / set / selected by the input unit 8, MR signal acquisition conditions, image data display conditions, PI imaging scan plan, desired magnification rate, Information such as the scan plan update mode is stored. On the other hand, the CPU of the main control unit 101, the magnitude of the pulse current supplied to the gradient coil 21 and the RF coil unit 30 based on the pulse sequence of the MR signal collection condition set in the input unit 8, the supply time, the supply timing, etc. Is supplied to the sequence control unit 102.

  The sequence control unit 102 includes a CPU and a storage circuit (not shown). After the pulse sequence information supplied from the main control unit 101 is temporarily stored in the storage circuit, a sequence control signal is generated based on the pulse sequence information. The gradient magnetic field power supply 22 and the transmission / reception unit 3 of the gradient magnetic field generation unit 2 are controlled. The top plate movement control unit 103 generates a top plate movement control signal based on a top plate movement instruction signal supplied from the input unit 8 via the main control unit 101 and supplies it to the top plate movement mechanism unit 5.

  Next, coil elements of the multichannel coil 302 selected based on the slice cross section of the PI imaging scan plan will be described with reference to FIGS. In the following, for the sake of simplicity, the multi-channel coil 302 having 16 coil elements arranged in a body axis direction (z direction) and four each in the x direction perpendicular to the body axis direction will be described. Although described, it is not limited to this.

  FIG. 4 shows a slice section (coronal section) of the PI imaging scan plan set for the positioning image data Dx of the subject 150 collected by pilot imaging. For example, FIG. In the positioning image data Dx shown in a), the arrangement region 302x of the multi-channel coil 302 (see FIG. 4B) with respect to the subject 150 is set, and is further inclined by an angle θ with respect to the body axis direction (z direction). The position of the slice slice Sx is set.

  When the above-described PI imaging scan plan is set in the positioning image data Dx, the sequence control unit 102 of the control unit 10 controls the gradient magnetic field power supply 22 so that the Xx direction of the slice cross section Sx becomes the phase encoding direction. . Then, four RF channels are formed by synthesizing MR signals detected from four coil elements (for example, 3e11 to 3e14) corresponding to the phase encoding direction based on a predetermined algorithm. As shown in FIG. 4B, the multichannel coil 302 used in PI imaging forms four sections 3s1 to 3s4 in the body axis direction (z direction) of the subject 150, and each of the sections 3s1 to 3s4. Has four coil elements. Then, the MR signal synthesis unit 33 of the transmission / reception unit 3 forms a plurality of RF channels by synthesizing the MR signals detected by these coil elements, and the RF channel selection unit 34 selects among the RF channels. M RF channels suitable for PI photography are selected. Hereinafter, a case where the number M of channels of the receiving unit 32 is 16 will be described.

  FIG. 5 shows a coil element of the multi-coil 302-1 or 302-2 that is used when the maximum magnification rate R for PI imaging is 4, and the selection in this case is based on the scan plan for PI imaging. It depends on the inclination angle θ with respect to the body axis direction (z direction) of the slice slice Sx to be set. That is, when the inclination angle θ of the slice section Sx with respect to the z direction is 45 degrees or less, the RF channel selection unit 34 detects the MR signals detected from the coil elements 3e11 to 3e14 in the section 3S1, as shown in FIG. Are combined to select four RF channels formed in the x direction, and further, the four RF channels formed in the x direction are combined by combining the MR signals detected from the coil elements 3e21 and 3e24 in the section 3S2. Select the RF channel.

  Similarly, the RF channel selector 34 performs the x-direction operation by combining MR signals detected from the coil elements 3e11 to 3e14 of the multi-coil 302-2 (not shown) and combining MR signals detected from the coil elements 3e21 to 3e24. Each of the four formed RF channels is selected.

  Then, the reconstruction processing unit 621 in the high-speed calculation unit 62 of the image data generation unit 6 reconstructs the diagnostic MR data obtained by the four RF channels selected in each section, and performs the pre-correction. The four diagnostic image data are generated, and the development processing unit 622 generates one diagnostic image data in which the four diagnostic image data RF are expanded and the aliasing is corrected.

  On the other hand, when the inclination angle θ of the slice cross section Sx with respect to the x direction is 45 degrees or more, the RF channel selection unit 34 is detected by the coil elements 3e11 to 3e41 in the sections 3S1 to 3s4 as shown in FIG. The four RF channels formed in the z direction are selected by combining the MR signals, and the four RF channels formed in the z direction by combining the MR signals detected by the coil elements 3e12 to 3e42. Select the RF channel.

  Similarly, the RF channel selection unit 34 performs the z-direction operation by combining MR signals detected from the coil elements 3e11 to 3e41 of the multi-coil 302-2 (not shown) and combining MR signals detected from the coil elements 3e12 to 3e42. Each of the four formed RF channels is selected. Then, the high-speed calculation unit 62 of the image data generation unit 6 reconstructs the diagnostic MR data obtained by the above-described RF channel selected in the z direction, and performs the four diagnostic image data before being corrected. The development processing unit 622 generates one piece of diagnostic image data in which the four diagnostic image data RF are subjected to a development process and the folding is corrected.

  As described above, the four pre-correction diagnostic image data generated based on the four RF channels formed in the direction (x direction or z direction) corresponding to the phase encoding direction Xx in FIG. By doing so, PI imaging with a maximum double speed R of 4 is possible without depending on the magnitude of the inclination angle θ of the slice cross section Sx.

  On the other hand, when the coil elements 3e14, 3e24, 3e34, and 3e44 are not present in the multichannel coil 302, the number of RF channels in the x direction is 3, and the maximum double speed R is 4 when the inclination angle θ of the slice cross section Sx is 45 degrees or less. PI shooting is impossible. That is, in order to realize PI imaging with a maximum double speed R of 4, it is necessary to update so that the inclination angle θ of the slice section Sx in the PI imaging scan plan is 45 degrees or more.

  Similarly, when there are no coil elements 3e41, 3e42, 3e43, and 3e44 in the multichannel coil 302, the number of RF channels in the z direction is 3, and the maximum double speed R is obtained when the inclination angle θ of the slice cross section Sx is 45 degrees or more. However, PI shooting of 4 is impossible. Therefore, in order to realize PI imaging with a maximum double speed R of 4, it is necessary to update the inclination angle θ of the slice section Sx in the PI imaging scan plan to 45 degrees or less.

  Next, FIG. 6 shows that when the maximum speed ratio R is 2, among the 16 coil elements 3eij (i = 1 to 4, j = 1 to 4) two-dimensionally arranged by the multichannel coil 302 described above. When the inclination angle θ of the slice cross section Sx with respect to the x direction is 45 degrees or less, as shown in FIG. 6A, for example, the coil element of the section 3s1 is shown. Two RF channels are formed in the x direction based on the MR signals detected in 3e11 and 3e12. Similarly, two RF channels are formed in the x direction for each of the sections 3s2 to 3s4. . Then, the image data generation unit 6 performs reconstruction processing and expansion processing on the MR signals obtained from the two RF channels formed in the x direction of each section, and generates diagnostic image data that does not return. .

  When the inclination angle θ of the slice cross section Sx with respect to the x direction is 45 degrees or more, as shown in FIG. 6B, for example, based on the MR signals detected in the coil element 3e11 of the section 3s1 and the 3e21 of the section 3s2. Thus, two RF channels are formed in the z direction, and two RF channels are formed in the z direction for each of the coil elements 3e12 and 3e22, 3e13 and 3e23, 3e14 and 3e24. The image data generation unit 6 performs reconstruction processing and expansion processing on the MR signals obtained from the two RF channels formed in the z direction, and generates diagnostic image data that does not return.

  In this case, by using the multi-channel coil 302 in which 16 coil elements 3eij (i = 1 to 4, j = 1 to 4) are two-dimensionally arranged, two RFs are provided in both the z direction and the x direction. Therefore, the channel can be set, and therefore PI imaging with the maximum double speed R of 2 can be performed without depending on the magnitude of the inclination angle θ with respect to the z direction of the slice cross section Sx.

(Update procedure for scan plans for PI photography)
Next, the update procedure of the PI photography scan plan will be described with reference to the flowchart of FIG. Prior to PI imaging of the subject 150, the operator of the MRI apparatus 200 selects multi-channel coils 302-1 and 302-2 having two-dimensionally arranged coil elements, and the multi-channel coils 302-1 and 302- are selected. 2 is arranged near the body surface and near the back surface of the subject 150 placed on the top 4. At this time, the arrangement information of the coil elements in the multichannel coils 302-1 and 302-2 is stored in the storage circuit in the main control unit 101 of the control unit 10 together with the identification information (step S1 in FIG. 7).

  Next, the operator inputs a top board movement instruction signal at the input unit 8 and moves the top board 4 in the body axis direction (z direction) so that the diagnosis target portion of the subject 150 is located in the imaging field at the center of the gantry. Further, the operator performs input of object information, setting of MR signal collection conditions and image data display conditions in pilot imaging and PI imaging, selection of a scan plan update mode, and the like at the input unit 8. In this embodiment, either the navigation update mode or the automatic update mode is selected as the scan plan update mode. These input information / setting information / selection information are also stored in the storage circuit provided in the main control unit 101 (step S2 in FIG. 7).

  When the above initial setting is completed, the operator inputs a pilot shooting start command signal for the purpose of collecting positioning image data at the input unit 8, and this command signal is input to the main control unit 101 of the control unit 10. Then, the generation of positioning image data is started.

  Hereinafter, a case where MR signal acquisition conditions for generating T1-weighted image data in the coronal cross section of the subject 150 as positioning image data using the SE (spin echo) method is set in the above-described step S2 will be described.

  When collecting T1-weighted image data by the SE method, the gradient magnetic field power supply 22 of the gradient magnetic field generation unit 2 shown in FIG. 1 is configured in the x direction based on the sequence control signal supplied from the sequence control unit 102 of the control unit 10. The pulse current for the gradient magnetic field coil 21 in the y direction and the z direction is controlled, and the slice selection gradient magnetic field Gs for setting the coronal section at the imaging target portion of the subject 150 and the MR signal obtained from the imaging slice section are used. A phase encode gradient magnetic field Ge and a read (frequency encode) gradient magnetic field Gr for encoding the generation position are applied.

  For example, when generating positioning image data having Na × Na pixels, the application of the phase encoding gradient magnetic field Ge having Na kinds of magnetic field strengths is repeated Na times in the repetition period TR, and a predetermined magnetic field strength is provided. The application of the read (frequency encoding) gradient magnetic field Ge is repeated in the repetition period TR.

  On the other hand, the transmission unit 31 of the transmission / reception unit 3 supplies a pulse current to the WB coil 301 of the RF coil unit 30 during the application of the first slice selection gradient magnetic field Gs to apply a 90-degree RF pulse to the imaging region of the subject 150. Further, the same part is irradiated with the 180-degree RF pulse during the application of the second slice selective gradient magnetic field Gs after the time TE / 2 from the irradiation. Next, the WB coil 301 and the reception unit 32 of the transmission / reception unit 3 receive the positioning MR signal generated from the subject 150 after time TE / 2 from the irradiation of the 180-degree RF pulse, and the data storage unit 61 of the image data generation unit 6. Is stored in the MR data storage unit 611.

  The 90-degree RF pulse and the 180-degree RF pulse described above are RF waves for supplying the nuclear spin with energy necessary for rotating the nuclear spin of the subject tissue by 90 degrees and 180 degrees, and the time TE is , The time from the irradiation of the 90-degree RF pulse until the MR signal is detected, TR is the MR signal detection period, and T1 is the longitudinal relaxation time of the nuclear spin of the living tissue.

  Then, if Na positioning MR signals are acquired by updating the magnetic field strength of the phase encoding gradient magnetic field Ge Na times, the reconstruction processing unit 621 in the high-speed calculation unit 62 of the image data generation unit 6 respectively Two-dimensional Fourier transform is applied to Na positioning MR signals having Na data points (ie, positioning MR data) to generate positioning image data having, for example, a coronal cross section having Na × Na pixels. Is displayed on the display unit 7 (step S3 in FIG. 7).

  An operator who has observed the positioning image data on the display unit 7 uses the input device provided in the input unit 8 to set a PI shooting scan plan in the positioning image data. Specifically, a slice section (for example, a coronal section) Sx is set in a predetermined direction based on the arrangement region 302x of the multichannel coil 302 superimposed on the positioning image data (see FIG. 4A) (see FIG. 4A). 7 (step S4), and a desired double speed ratio for SI shooting is set (step S5 in FIG. 7). These pieces of setting information are stored in the storage circuit of the main control unit 101.

  On the other hand, the PI imaging determination unit 9 uses the preset channel number information of the receiving unit 32, the arrangement information of the coil elements in the multichannel coil 302, and the slice cross-section information set for the positioning image data as the main control unit. 101 is read from the storage circuit 101, and the maximum speed ratio is calculated based on these pieces of information (step S6 in FIG. 7). Further, the PI photographing determination unit 9 determines the possibility of PI photographing at the desired double speed ratio by comparing the calculated maximum double speed ratio with the desired double speed ratio read from the storage circuit (FIG. 7). Step S7).

  When it is determined that PI imaging at a desired double speed rate is possible, the determination result is supplied to the main control unit 101, and the main control unit 101 that has received the determination result uses the desired double speed rate for each unit of the MRI apparatus. A PI control is executed by supplying a control signal for starting PI shooting (step S11 in FIG. 7).

  On the other hand, if it is determined in step S7 that the PI update at the desired double speed rate is impossible in the state in which the navigation update mode is selected in the initial setting in step S2, the scan plan item to be updated to enable the PI shooting ( For example, the slice section direction) is retrieved and displayed on the display unit 7 (step S8 in FIG. 7). Next, the operator updates the PI imaging scan plan based on the displayed scan plan item (step S9 in FIG. 7). Then, steps S6 to S9 are repeated based on the updated PI shooting scan plan until it is determined that PI shooting is possible (steps S6 to S9 in FIG. 7).

  In addition, when it is determined that PI shooting at a desired double speed rate is impossible in the state where the automatic update mode is selected in the initial setting, the PI shooting scan plan that makes PI shooting impossible is automatically updated (see FIG. 7). In step S10), the main control unit 101 performs PI imaging based on the updated scan plan (step S11 in FIG. 7).

  According to the embodiment of the present invention described above, when performing PI imaging on the subject based on the PI imaging scan plan set in advance by positioning imaging data by pilot imaging, PI imaging at a desired double speed ratio is performed. It is possible to automatically select a coil element of a suitable multi-channel coil that can be made based on the scan plan for PI photography.

  In the MRI apparatus in the above-described embodiment, the possibility of PI imaging at a desired double speed rate is determined based on the arrangement information of the coil elements and the information of the PI imaging scan plan. It is possible to automatically update the PI photography scan plan to be updated or notify the operator. For this reason, it is possible to collect high-quality diagnostic image data without depending on the skill of the operator. Further, since the number of re-takings of PI imaging is reduced, the inspection efficiency is greatly improved and the burden on the operator is reduced. The

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified. For example, in the above-described embodiment, the case where two-dimensional image data having a coronal section as a slice section is described. However, two-dimensional image data having a sagittal section or an axial section as a slice section may be generated. . In addition, the RF coil unit 30 has been described as having the multi-channel coil 302-1 disposed near the body surface of the subject 150 and the multi-channel coil 302-2 disposed near the back surface. It may have, and may have a plurality of multichannel coils near the body surface or near the back surface.

  Furthermore, the present invention can also be applied to the collection of MR signals when collecting volume data of the subject 150 and performing predetermined signal processing on the volume data to generate three-dimensional image data. In this case, the phase encoding is set not only in the application direction (phase encoding direction) of the phase encoding gradient magnetic field Ge but also in the application direction (slice encoding direction) of the slice selection gradient magnetic field Gs. Therefore, the time required for collecting the volume data can be greatly shortened by thinning out the phase encoding steps in these directions.

  On the other hand, in the above-described embodiment, a case has been described in which it is determined that PI shooting at a desired double speed ratio is impossible, and a scan plan item to be updated is notified to the operator, but the number and arrangement of coil elements are different. The operator may be notified of information regarding the update to the multi-channel coil or the update to a suitable double speed ratio.

  In the above-described embodiments, the case where the positioning image data is generated by pilot imaging using the SE method has been described. However, the FSE (fast SE) method, the EPI (echo planar imaging) method, the FE (gradient echo) method. The positioning image data may be generated by applying another pulse sequence such as a method. Furthermore, in the above-described embodiment, the method for correcting the aliasing by developing the plurality of image data obtained by the reconstruction process has been described. However, the MR data before the reconstruction process is corrected and the aliasing is corrected. A reduction method may be used.

  Furthermore, the case where the PI shooting determination unit 9 determines that PI shooting at the desired double speed ratio is impossible has been described on the case where the scan plan item or the like to be updated is displayed on the display unit 7, but the present invention is not limited to this. For example, it may be displayed or notified by other notification means such as a display panel provided in the input unit 8.

1 is a block diagram showing the overall configuration of an MRI apparatus in an embodiment of the present invention. The block diagram which shows the structure of the RF coil unit with which the MRI apparatus of the Example was equipped, and the transmission / reception part. The figure which shows the structure of the multichannel coil used in the Example. The figure for demonstrating the specific example of the scan plan for PI imaging | photography in the Example. The figure which shows the specific example of the coil element selected when the maximum speed ratio is 4 in the Example. The figure which shows the specific example of the coil element selected when the maximum speed ratio is 2 in the Example. 6 is a flowchart showing a procedure for updating a PI photography scan plan in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field generation part 11 ... Main magnet 12 ... Static magnetic field power supply 2 ... Gradient magnetic field generation part 21 ... Gradient magnetic field coil 22 ... Gradient magnetic field power supply 3 ... Transmission / reception part 31 ... Transmission part 32 ... Reception part 33 ... MR signal synthetic | combination part 34 ... RF channel selection unit 30 ... RF coil unit 301 ... WB coils 302-1 and 302-2 ... multi-channel coil 4 ... top plate 5 ... top plate moving mechanism unit 6 ... image data generation unit 61 ... data storage unit 611 ... MR Data storage unit 612 ... Image data storage unit 62 ... High-speed calculation unit 621 ... Reconstruction processing unit 622 ... Development processing unit 7 ... Display unit 8 ... Input unit 9 ... PI shooting determination unit 10 ... Control unit 101 ... Main control unit 102 ... Sequence control unit 103 ... top plate movement control unit 200 ... MRI apparatus

Claims (7)

An MR signal of a plurality of RF channels formed by irradiating a subject to which a static magnetic field and a gradient magnetic field are applied with an RF pulse and synthesizing MR signals from the subject detected by a plurality of coil elements. In an MRI apparatus for performing parallel imaging (PI) imaging based on
MR signal synthesis means for synthesizing MR signals detected by the coil elements to form a plurality of RF channels;
Scan plan setting means for setting a PI imaging scan plan for positioning image data collected in advance by pilot imaging of the subject;
A speed ratio setting means for setting a desired speed ratio for the PI shooting;
The plurality of RF channels suitable for the PI imaging are selected from the plurality of RF channels formed by the MR signal synthesizing unit based on the information on the scan plan for PI imaging and the information on the desired double speed ratio. An MRI apparatus comprising an RF channel selection means.   PI imaging determination means and notification means, and the PI imaging determination means determines the possibility of PI imaging at the desired double speed ratio based on the RF channel information and the PI imaging scan plan information, and is impossible 2. The MRI apparatus according to claim 1, wherein if it is determined, at least one of information on a PI imaging scan plan, an RF channel, and a desired double speed ratio to be updated is notified by the notification unit.   PI imaging determination means is provided, and the PI imaging determination means determines the possibility of PI imaging at the desired double speed ratio based on the information on the RF channel and the information on the scan plan for PI imaging, and determines that it is impossible. 2. The MRI apparatus according to claim 1, wherein the PI imaging scan plan to be updated is automatically updated.   3. The PI imaging determination unit determines the possibility of PI imaging at the desired double speed ratio based on information on the RF channel and a slice cross-sectional direction in the PI imaging scan plan. Item 4. The MRI apparatus according to Item 3.   The PI photographing determination means compares the desired double speed ratio set by the double speed ratio setting means with the maximum double speed calculated based on the information on the RF channel and the information on the scan plan for PI photographing. 4. The MRI apparatus according to claim 2, wherein the possibility of PI imaging at a double speed rate is determined.   The RF channel selection means includes the plurality of RF channels that enable PI imaging at the desired double speed ratio based on the slice section direction in the PI imaging scan plan and the array information of the coil elements that are two-dimensionally arranged. The MRI apparatus according to claim 1, wherein the MRI apparatus is selected.   2. The MRI apparatus according to claim 1, wherein the RF coil selection means selects the plurality of RF channels corresponding to the number of channels of a receiving circuit that processes the MR signal.

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